DESCRIPTION:(adapted from applicant's abstract) The long-term goal of this project is to develop a new clinical test that can identify and characterize the severity of an asymmetry of vestibular function between the two ears. Preliminary results suggest that a test based on measurement of vestibulo-ocular reflex (VOR) eye movements evoked by a novel rotational stimulus can overcome the significant limitations of the two main clinical tests (caloric and conventional rotation) currently used to evaluate vestibular function. If proven effective, this diagnostic test could be rapidly adopted into clinical practice since rotation test equipment capable of delivering the proposed new rotational stimulus is currently in used in most major medical centers. There are three specific aims in the proposal. The first aim is to use modeling and simulation studies to investigate how physiological properties of vestibular-nerve afferents and VOR are likely to influence the ability of the new rotational stimulus to accurately identify a vestibular asymmetry. These properties include static and dynamic characteristics of primary semicircular canal afferents, orientation of the semicircular canals with respect to one another and with respect to the rotation axis, and dynamic characteristics of nystagmus generated in response to large amplitude rotational motions. The second aim is to use experimental studies to determine exact specifications for the new rotational stimulus, and to investigate methodological factors that influence the sensitivity of the new test. The third aim is to verify the clinical applicability of the proposed new test by comparing results from caloric and conventional rotation tests with results from the proposed new rotation test. Experimental results from subjects with different levels of partial unilateral vestibular loss will determine the effectiveness and reliability of the proposed new rotation test.